1. Field of the Invention
The present invention pertains to helical scan recording, and particularly to helical scan tape drives which accommodate a single-reel tape cartridge.
2. Related Art and Other Considerations
In magnetic recording on tape using a magnetic tape drive, relative motion between a head unit (typically with both a write element and a read element) and the tape causes a plurality of tracks of information to be transduced with respect to the tape. The magnetic tape is typically housed in a cartridge which is loaded into the tape drive. The tape extends between a supply reel and a take-up reel.
In a helical scan recording and reproduction arrangement, as the magnetic tape is transported the magnetic tape is at least partially wrapped around a rotating drum (sometimes referred to as a xe2x80x9cscannerxe2x80x9d or xe2x80x9crotorxe2x80x9d) so that heads (both write heads and read heads) positioned on the drum are contiguous to the drum as the drum is rotated. In a recording operation, one or more write heads on the drum physically record data on the tape in a series of discrete stripes oriented at an angle with respect to the direction of tape travel. The data is formatted, prior to recording on the tape, to provide sufficient referencing information to enable later recovery during readout by one or more read heads. Examples of helical scan tape drives are shown, inter alia, in the following US patents (all of which are incorporated herein by reference): U.S. Pat. No. 4,835,628 to Hinz et al.; U.S. Pat. No. 4,843,495 to Georgis et al.; U.S. Pat. No. 5,065,261 to Hughes et al.; U.S. Pat. No. 5,068,757 to Hughes et al.; U.S. Pat. No. 5,142,422 to Zook et al.; and U.S. Pat. No. 5,602,694 to Miles et al. (which discloses a capstanless helical scan tape drive).
Historically, helical scan tape drives utilize tape cartridges or cassettes that incorporate two coplanar enclosed reels. These dual reel tape cartridges internally house both a supply reel and a take-up reel. After the cartridge is loaded into the tape drive, the tape is extracted by mechanisms in the drive so that a segment of the tape is pulled from the cartridge and into a tape path that travels proximate the head unit. The extraction mechanisms take the form of tape guides which are mounted on trolleys. During the extraction operation, trolley motors move the trolleys along a predefined trolley path, so that the tape guides which surmount the trolleys displace the tape into the tape path as the trolleys travel along the trolley path. When the trolleys reach the full extent of travel along the trolley path, the tape is proximate the head unit. Thereafter the tape can be transported past the head unit, e.g., by activation of a capstan and/or the supply reel and take-up reel motors, depending upon the particular type of transport mechanisms employed.
Dual reel tape cartridges such as that described above require a relatively large plan area. Consequentially, dual reel tape cartridges are not well-suited to deep, small area form factor shapes (e.g., such as the 5.25 inch full high form factor known in the data storage industry).
There are types of tape cartridges other than dual reel tape cartridges. For example, an IBM 3480-type magnetic tape cartridge is a single reel, tape cartridge that has a leader block attached to one end of the tape. The leader block protrudes from or is otherwise situated so that a tape transport mechanism can grasp the leader block and thread the leader block end of the tape over a path to a take-up reel. The tape path includes a plurality of bearings for guiding the tape. The take-up reel usually includes a slot for receiving the leader block and is connected to an associated drive mechanism which transports the tape between the take-up reel and the tape cartridge.
U.S. Pat. No. 5,128,815 describes various other approaches to tape loading using single reel tape cartridges. In one approach, a leader tape is used in lieu of a leader block. According to U.S. Pat. No. 5,128,815, the leader tape follows a complex tape threading path around associated heads to the take-up reel. As the leader tape traverses the entirety of this complex tape threading path, the narrower magnetic tape is also pulled through the tape threading path and physically wrapped around a rotary head.
An alternative helical scan data storage arrangement described as prior art in U.S. Pat. No. 5,128,815 utilizes a two reel cassette having its reels placed coaxially, one over the other, necessitating an angled tape path within the tape cassette between the two reels to transport the tape between the two reels.
U.S. Pat. No. 5,128,815 itself concerns an IBM-3480-type single reel tape cartridge that is handled in such a way to create a xe2x80x9cvirtualxe2x80x9d dual reel tape cassette. The tape handling involves a two step process. In the first step, a tape end (e.g., leader block) is withdrawn from the single reel tape cartridge and moved to be attached to the take-up reel (thereby effectively forming a dual reel tape cartridge). In the second step, other tape guiding elements withdraw the tape further from the virtual tape cassette, bringing the tape into contact with the helical scanner in a manner similar to other self-threading helical drives using conventional dual reel cartridges. Yet the virtual dual reel tape cassette still requires a relatively large plan area, as the second tape reel (i.e., the take-up reel), although not part of the tape cartridge, is coplanar with the single reel (i.e., the supply reel) of the IBM-3480-type cartridge.
U.S. Pat. No. 5,303,809 and U.S. Pat. No. 5,374,003 show variations of tape threading for a virtual tape cassette. Some of the variations in U.S. Pat. No. 5,374,003 involve use of an elevator to raise or lower the coplanar arrangement of the single reel of the cartridge and the take-up reel to another plane at which the threading path is located. However, all variations have the single reel of the IBM-3480-type cartridge and the take-up reel as being coplanar at all times. Hence, these variations consistently require the relatively large plan area, as discussed above.
What is needed, therefore, and an object of the present invention, is a tape drive that accommodates a single reel tape cartridge within a small area form factor shape.
A helical scan tape drive has a cartridge compartment for accommodating a single reel cartridge of magnetic tape, and a take-up reel which, with respect to a threading path, is not coplanar with the cartridge compartment. A threading system grasps an end of the magnetic tape in the cartridge and transports the magnetic tape through the threading path. The threading path is configured such that the magnetic tape is at least partially wrapped around a rotatable scanner before the end of the magnetic tape is attached to the take-up reel. The rotatable scanner has one or more elements for transducing information relative to the magnetic tape.
The take-up reel is situated at a location either above or below the cartridge compartment for reducing footprint of the drive. In one embodiment, the take-up reel and the cartridge compartment are in an at least partially overlapping relationship, e.g., with respect to a planar extension of at least one side wall of the cartridge compartment. The magnetic tape in the single reel cartridge (accommodated in the cartridge compartment) travels in a single reel plane when the magnetic tape is wound or unwound in the single reel cartridge; the magnetic tape on the tape-up reel travels in a take-up reel plane when the magnetic tape is wound or unwound relative to the take-up reel. In an illustrative embodiment, the single reel plane and the take-up reel plane are skew planes. A single reel plane intersection is formed by an intersection of the single reel plane with a plane perpendicular to a bottom wall of a cabinet, while a take-up reel plane intersection is formed by an intersection of the take-up reel with the plane perpendicular to a bottom wall of a cabinet. The single reel plane intersection and the take-up reel plane intersection are preferably angularly inclined relative to one another at an acute angle.
The threading system comprises a threading guide and a threading carriage. The threading guide grasps an end of the magnetic tape in the cartridge and carries it along the threading guide, thereby withdrawing the tape from the cartridge. Preferably the threading guide forms a non-planar threading path. In an illustrated example embodiment, the threading carriage is suspended below the threading guide. In such embodiment, the threading guide has a first end proximate the cartridge compartment and a second end proximate the take-up reel. The first end of the threading guide is essentially parallel to the single reel plane; the second end of the threading guide is essentially parallel to the take-up reel plane.
Plural guide elements contact the tape as the threading system transports the magnetic tape through the threading path. The plural guide elements include at least one stationary guide element and at least one movable guide element. After the magnetic tape is attached to the take-up reel, at least one moveable guide element is actuated to increase a degree of wrap of the magnetic tape about one or more of the stationary guide elements.